In the prior art, applicant is aware of several patents which issued to Aune et al. the particulars of which follow, which teach that it is known to use x-ray radiators and detectors positioned on either side of a piece of lumber for detecting defects in the lumber based on variation of detected density as the lumber is passed between the radiation source and the detector:
In the prior art, applicant is aware of U.S. Pat. No. 4,941,357 which issued to Schajer on Jul. 17, 1990 for a Method for Estimating the Strength of Wood wherein a method is described for measuring the longitudinal density profile of a piece of wood so as to allow estimation of the strength or stiffness of the wood by determining the clear wood and identifying structural defects by sharp density increases caused by knots. Applicant is also aware of U.S. Pat. No. 5,023,805 which issued to Aune et al. on Jun. 11, 1991 for a Log Scanner wherein it is taught to analyze a log containing knots by passing electromagnetic energy through the log and sensing the amount of energy passing through by sensors mounted opposite to the energy source. For asymmetric bodies at least two sources of electromagnetic energy are employed providing then for the longitudinal plans to be analyzed to identify the same different density element in each of the plans and to then reconstruct the log with the detected elements positioned in cross sections of the log. Applicant is also aware of U.S. Pat. No. 4,879,752 which issued to Aune et al. on Nov. 7, 1989 for a Lumber Optimizer wherein a lumber optimizer system is described which detects wane in a flitch by detecting the amount of electromagnetic radiation passing through localized areas of the flitch board to determine local differences in density and thereby a density profile of the flitch. A computer is employed to provide a profile of signal strengths generated by the detectors corresponding to the electromagnetic radiation sources, the computer generating an image of varying intensity depending on the signal, that is density for each discreet area of the flitch and to provide a density map. Defects, including their nature and position are determined from analysis of the map.
Applicant is also aware U.S. Pat. No. 5,394,342 which issued to Poon on Feb. 28, 1995 for an invention entitled Log Scanning. Poon teaches to scan the length of a log to provide a longitudinal density scan. Density peaks are plotted to form an image and adjacent peaks in adjacent rows and columns of pixels in the detectors are joined to provide an image depicting spines of detected knots, reprocessing then providing for determination of knot boundaries.
In the prior art applicant is also aware of U.S. Pat. Nos. 6,272,437 and 6,594,590 which issued on Aug. 7, 2001 and Jul. 15, 2003 respectively to Woods et al. for a Method and Apparatus for Improved Inspection and Classification of Attributes of a Workpiece. Woods et al disclose detecting the probable existence, location and type of defects in a work piece by generating a work piece model based on the signals produced by a sensor subsystem and merging signals from a plurality of such sensor subsystems by the use of a defect assembler. Defects are verified by combining the different results of automatic inspection into a single model.
What is neither taught nor suggested in the prior art, and which is an object of the present invention to provide, is a method and apparatus for determining the displaced size of a knot in a piece of lumber. As known in the prior art, knots typically have a higher density than the surrounding clear wood of the lumber piece, and that the change in density between clear wood and knot may be measured directly using x-ray radiation, that is, by detecting the intensity of x-ray radiation which impinges an x-ray sensor positioned on an opposite side from a radiation source of known intensity.